This invention relates generally to surface acoustic wave devices (SAW) and more particularly to a SAW device having improved frequency stability.
As is known in the art, surface acoustic wave devices are used in a variety of applications. In one such application, a surface acoustic device such as a SAW resonator is used in a feedback circuit of an amplifier to provide a frequency stabilized oscillator. It is also known in the art that SAW devices are commonly packaged to isolate the surface acoustic wave device from an external environment. Generally, during packaging of SAW devices, the process of sealing the SAW device packages induces frequency shifts, as well as, variations or uncertainties in frequency shift from the initial or design frequency of the SAW device. For applications such as high precision, SAW resonator stabilized oscillators, frequency shifts of the order induced during sealing are often unacceptable. A further problem, however, is the uncertainty in the frequency shift on sealing. A large uncertainty in frequency shift makes compensation for such frequency shift more difficult, since this uncertainty prevents a designer from compensating for the frequency shift by designing the device for a lower or higher frequency and thus taking into consideration the post seal frequency shift.